The invention relates to a laser-machining apparatus, possessing a device for effecting the circular polarization or elliptical polarization of the laser beam, this device comprising a mirror assembly for effecting the linear polarization of the laser beam at an angle of, for instance, 45.degree. to the vertical.
In known laser equipment of this type, the device for effecting the circular or elliptical polarization of the laser beam comprises, on the one side, a mirror arrangement for effecting the linear polarization of the laser beam which emerges from the resonator and, on the other side, comprises an optical arrangement for shifting the phase position of a partial beam by 1/4 of a wavelength in relation to the other partial beam. In order to enable a circular or elliptical polarization to result, in the latter arrangement, by superposition, the plane of polarization of the laser beam entering this arrangement must be inclined at 45.degree. to the vertical. When the laser beam is unpolarized, the arrangement, in such an angular position, of the mirror assembly provided for effecting the linear polarization presents no problems. However, a mirror assembly of this nature is expensive, and the more so when account is taken of the ongoing maintenance and replacement costs. These expenses are not eliminated even when use is made of a resonator from which the laser beam emerges in a polarized state, because the plane of polarization must then be rotated in a manner such that it is located in the desired angular position with respect to the vertical.
The object underlying the invention is to reduce this expenditure.
The object of the invention is achieved when the mirror assembly for effecting the linear polarization of the laser beam is formed by folding mirrors which are installed inside the resonator, and the latter is arranged in a manner such that a plane of reflection of the folding mirrors lies at 45.degree. to the vertical.
On account of its size, and on account of the design-related relationships with the auxiliary components, the resonator is the main component which clearly conditions the construction of the apparatus. In the technology relating to the design of a laser apparatus, the starting assumption has hitherto been made to the effect that the position of the resonator is chosen in order to satisfy design-related aspects alone, since the comparatively lightweight, small and adaptable optical components can thereafter be adapted, without problems, to suit the position of the resonator. For this reason, when folded resonators were used, the positioning of the plane of reflection of the folding mirrors, in one of the principal design directions, namely in the vertical plane, or in the horizontal plane, apparently formed part of the abovementioned starting assumption, as a precondition which could not be overturned. Accordingly, the invention is based on the underlying concept according to which the small and adaptable optical elements should not be adapted to suit the main component of the apparatus, but vice versa, namely to adapt the positioning of the main component to the optical components which are located downline, thereby achieving considerable savings and simplifications both in construction and operation.
In the context of the invention, the term folding mirror should be understood as embracing not only mirrors which, in pairs, effect a reversal of the beam, in each case parallel to themselves, as occurs in the case of folded resonators in a comparatively narrow sense, but should, rather, also embrace any other mirrors which may be installed inside a resonator and which effect a polarizing reversal of the beam.
It can be very expedient if the plane of reflection of the resonator is rotatable, so as to be able to adjust the plane of polarization or, as the case may be, the direction of the major axis of an elliptically polarized beam cross-section, to suit any desired conditions.
Citing an angle of 45.degree. should not be understood as a narrow limitation, and should also include those deviations from this angular value which might, in a particular case, be due, for example, to a deviation of the working direction of the laser beam from the vertical.
In the following text, the invention is explained in more detail, by reference to the drawing, which diagrammatically illustrates an example of the apparatus arrangement according to the invention. In this drawing: